The successful completion of the human genome project and mapping of many disease genes, combined with advances in the molecular understanding of gene-expression pathways, provides unprecedented opportunities to design novel mechanism-based therapies for various genetic diseases. Nonsense mutations account for a large fraction of the causal mutations in nearly all genetic diseases. By definition, nonsense mutations introduce premature termination codons (PTCs), resulting in truncated proteins, and usually severe disease presentations. Translational readthrough drugs, such as ataluren, allow the synthesis of some full-length, functional protein from defective genes with nonsense mutations. However, nonsense-mediated mRNA decay (NMD)a ubiquitous mRNA quality-control pathwaydiminishes the effectiveness of readthrough drugs. We will selectively abrogate NMD of mRNAs harboring PTCs, so as to increase their availability for readthrough drugs. To explore the feasibility of our approach, we will initially focus on cell-culture experiments with several nonsense alleles of CFTR, MECP2, DMD, and HBB genes, which cause cystic fibrosis, Rett syndrome, Duchenne muscular dystrophy, and beta-thalassemia, respectively. We will systematically test the effect of inhibiting NMD on mRNA accumulation. Using reporter cell lines, we will then combine transcript-specific NMD inhibition with ataluren treatment, and determine whether there is increased synthesis of full-length protein, compared to ataluren treatment alone. The results of this exploratory study are expected to provide proof of principle for the effectiveness of targeted inhibition of NMD to enhance the efficacy of readthrough drugs. The proposed experiments could lead to a broadly applicable therapeutic approach that would be used in combination with readthrough drugs to treat a large number of severe genetic diseases. PUBLIC HEALTH RELEVANCE: Nonsense mutations result in truncated protein production and cause many severe genetic diseases. Drugs like ataluren can promote the synthesis of intact proteins from genes with nonsense mutations; however, cells have an intrinsic mechanism that diminishes the output of genes with nonsense mutations. We will develop a method to bypass this mechanism for individual mutant genes, so as to enhance the effectiveness of ataluren and similar drugs, and thereby provide more effective therapies for a variety of genetic diseases.